A description is given of MILVIT, a model for forecasting outbreaks of downy mildew Results of validation studies carried out in Champagne, France, during 1991-93 showed that the model correctly predicted the main stages of the epidemic such as symptom appearance and sporulation. Its use enabled a reduction in number of fungicide treatments by c. 2 per year without prejudicing disease control. Following these studies, MILVIT was incorporated into the agricultural warning service in 1994.